1. Field of the Invention
The present invention relates to a display device, and more particularly, to a liquid crystal display device and a method of fabricating the same. Although the present invention is suitable for a wide scope of applications, it is particularly suitable for facilitating hardening of a photo-hardening sealant without modifying a black matrix layer pattern or increasing a size of the substrate.
2. Discussion of the Related Art
Generally, a liquid crystal display device has characteristics, such as low-voltage driving, low power consumption, full-color implementation, thin and compact size, and the like. Thus, it has been widely used for calculators, notebook computers, electronic watches, computer monitors, aircraft gauges, personal mobile terminals, and mobile phones.
Screens of liquid crystal display devices are becoming wider and larger in size. When a wide-screen liquid crystal display is fabricated by a liquid crystal injection method, it takes too much time. For this reason, a liquid crystal dropping method has been widely used to form a liquid crystal layer. The liquid crystal dropping method includes the steps of dropping liquid crystals on a substrate before bonding two substrates, forming a photo-hardening sealant, bonding the substrates, and hardening the sealant.
The photo-hardening sealant includes a photo-hardening sealant, which becomes a radical when UV-ray is applied thereto, and a single solution type sealant mixed with acrylate polymerized by the photo-hardening sealant. Hence, in order to harden the photo-hardening sealant, a portion where the sealant is disposed is exposed to UV-ray.
Moreover, the liquid crystal dropping method uses a column spacer attached to the substrate instead of a ball spacer dispersed on the substrate to obtain a uniform cell thickness.
A liquid crystal display device and a method of fabricating the same are explained by referring to the attached drawings as follows.
FIG. 1A illustrates a layout of a thin film transistor array substrate for a related art liquid crystal display device. FIG. 1B illustrates a cross-sectional view taken along line IB—IB in FIG. 1A.
As shown in FIG. 1A, a plurality of gate and data lines 80 and 90 are formed on an active area 120 of a thin film transistor array substrate 100 to cross each other and define a plurality of pixel areas. A pixel electrode 112 is formed at each of the pixel areas. And, a plurality of thin film transistors (not shown) are formed at each intersection between the gate and data lines 80 and 90 and apply signals of the data lines 90 to the pixel electrodes 112 by being turned on/off through signals of the gate lines 80, respectively.
A common line 140 is formed at the circumference of the active area 120 to provide a common electrode on a color filter array substrate (not shown) with a common voltage. And, a plurality of silver (Ag) dots (not shown) are formed at the common line 140 for electrical connections to the common electrode on the color filter array substrate.
Moreover, a column spacer 105 is formed on the gate or data line 80 or 90 to maintain a uniform cell gap. And, a photo-hardening sealant 110 is formed at the circumference of the active area 120 to surround the active area 120 for bonding the thin film array substrate and the color filter array substrate to each other. In this case, the photo-hardening sealant 110 is partially formed on the common line 140.
Hence, in order to bond the substrates with the photo-hardening sealant 110 and to fix the photo-hardening sealant 110 thereto, UV-ray is applied from the color filter array substrate side or a thermo-hardening sealant is used instead of the photo-hardening sealant.
When the UV-ray is applied from the thin film transistor array substrate side, the UV-ray cannot be applied to the photo-hardening sealant 110 on the common line 140, thereby degrading the adhesion since the photo-hardening sealant 110 is not hardened completely.
In FIG. 1B, an insulating layer 141 to form a gate insulating layer and a passivation layer is formed on the common line 140, and the photo-hardening sealant 110 is deposited on the insulating layer 141. Since the insulating layer 141 is transparent, the UV-ray is transmitted. However, since the common line 140 is opaque, the UV-ray is cut off by the common line 140. Hence, the photo-hardening sealant 110 cannot be hardened by the UV-ray, thereby weakening the adhesion.
A related art method of fabricating a liquid crystal display device using a liquid crystal dropping method is explained in detail as follows.
FIGS. 2A to 2G illustrate layouts and cross-sectional views of a related art fabricating process of a liquid crystal display device.
In the method of fabricating a liquid crystal display device using a liquid crystal dropping method, a plurality of liquid crystal display panel is designed on a mother substrate. More specifically, a plurality of liquid crystal display panels are designed on the mother substrate to form a thin film transistor array and a color filter array on each of the corresponding substrates. Liquid crystals are dispensed on the substrate. A sealant is deposited on the substrate, and the substrates are bonded to each other. The bonded substrates are then cut into a plurality of unit liquid crystal display panels. A plurality of the liquid crystal display panels designed on a single substrate will be explained in the following descriptions.
Although not shown in FIG. 2A, a plurality of gate and data lines are arranged on a first substrate 100 to cross each other and define a plurality of pixel areas. A pixel electrode (not shown) is formed on each of the pixel areas. A plurality of thin film transistors (not shown) are formed at each intersection between the gate and data lines to apply signals of the data lines to the pixel electrodes by being turned on/off through signals of the gate lines. A common line (not shown) is formed on the first substrate 100 to supply a common electrode with a common voltage. Herein, a plurality of liquid crystal display panels 99 are arranged on the first substrate 100.
Subsequently, a plurality of silver (Ag) dots 101 are formed on the common line of each of the liquid crystal display panels 99 to be electrically connected thereto.
As shown in FIG. 2B, liquid crystals 103 for the size of each liquid crystal display panel 99 is dropped on each of the liquid crystal display panels 99 of the first substrate 100.
As shown in FIG. 2C, a photo-hardening sealant 110 is deposited at the circumference of each liquid crystal display panel 99 of the first substrate 100.
As shown in FIG. 2D, a plurality of column spacers 105 are formed on a second substrate having a black matrix layer (not shown), a color filter layer (not shown), and a common electrode (not shown) formed thereon. And, the second substrate 150 is turned over to be placed over the first substrate 100.
Namely, the overturned second substrate 150 is fixed to an upper stage 170, which enables movement in the Z-axis direction (i.e., vertical direction), of a bonding machine having a controllable vacuum chamber. And, the first substrate 100 is fixed to a lower stage 160, which enables movement in the XY-axes direction (i.e., horizontal direction), of the bonding machine.
As shown in FIG. 2E, the first substrate 100 fixed to the lower stage 160 and the second substrate 150 fixed to the upper stage 170 are aligned. Then, the inside of the bonding machine is pumped down to have a desired vacuum condition. Hence, the first and second substrates 100 and 150 are bonded to each other. The first and second substrates 100 and 150 do not contact each other so as to form a first gap between the substrates 100 and 150.
As shown in FIG. 2F, after both of the substrates are bonded to have the first gap, a gas or air is injected into the bonding machine under a vacuum condition to provide the inner space of the bonding machine with the atmospheric pressure. Since the space between the bonded substrates is in a vacuum state and the surrounding is in the atmospheric pressure, both of the substrates are pressurized by a difference between the pressure within the gap between the first and second substrates and the atmospheric pressure. In this case, both of the substrates are pressurized to have a cell gap by the column spacers 105. Hence, the liquid crystals 103 are spread between the substrates to form a liquid crystal layer 103a. 
As shown in FIG. 2G, UV-ray is applied from the side of the second substrate 150 to harden the photo-hardening sealant 110.
However, the related art liquid crystal display device and the method of fabricating the same have the following problems or disadvantages.
Since the common line on the first substrate blocks the UV-ray, the UV-ray should be applied to the first substrate from the upper side instead of the lower side.
Furthermore, when the UV-ray is applied from the upper side of the substrate, either a pattern of the black matrix layer is modified or the size of the substrate is increased, thereby misaligning the sealant from the black matrix layer.